1. Field of the Invention
The invention relates to the delivery of Internet Protocol (IP) content over cable systems using a standard protocol Data Over Cable System Interface Specification (DOCSIS). More particularly, the invention relates to transmitting IP content within systems involving Cable Modem Termination System (CMTS) architecture and processing.
2. Description of the Related Art
Most cable systems currently provide video (and data) content delivery services via digital broadcast. The video image is first digitized, and then compressed, e.g., via one of several digital algorithms or compression standards, such as the MPEG2 (Moving Pictures Expert Group) algorithm or the MPEG4 part 10 algorithm, where the latter also is known as the International Telecommunications Union (ITU) H.264 standard. These compression standards allow the same video content to be represented with fewer data bits. Using MPEG2, standard definition television currently can be transmitted at a rate of approximately 4 Megabits per second (Mbps). Using MPEG 4 Part 10, the same video content can be transmitted at a rate of approximately 2 Mbps. The digital video content typically is transmitted from a source at a cable provider's headend to one or more network elements, such as an end user's set-top box (or other suitable video processing device), via a digitally modulated radio frequency (RF) carrier, with the video content organized into an MPEG2 Transport Stream (MPEG2-TS) format.
Cable system operators are considering Internet Protocol (IP)-based methods for delivery of content, such as IP-video and IP Television (IPTV), to supplement their current digital video delivery methods. The internet protocol is not required for MPEG2 Transport Streams. However, IP-based video delivery allows the possibility of new video sources, such as the Internet, and new video destinations, such as end user IPTV playback devices. If cable systems do include IP-based content delivery, it is quite possible and likely that relatively large amounts of bandwidth will be needed to deliver IPTV content to end users. Moreover, as end users continue to shift their viewing desires toward on-demand applications, a relatively large percentage of such on-demand content likely will be IPTV content.
To cope with the anticipated surge of IPTV viewing, the cable industry developed the Data Over Cable System Interface Specification (DOCSIS®) standard or protocol, including the DOCSIS 3.0 standard. In general, DOCSIS defines interface requirements for cable modems involved in high-speed data distribution over cable television system networks. The cable industry also developed the Cable Modem Termination System (CMTS) architecture and the Modular CMTS (M-CMTS™) architecture for this purpose. In general, a CMTS is a component, typically located at the headend or local office of a cable television company, that exchanges digital signals with cable modems on a cable network.
In general, an EdgeQAM (EQAM) or EQAM modulator is a headend or hub device that receives packets of digital content, such as video or data, re-packetizes the digital content into an MPEG transport stream, and digitally modulates the digital transport stream onto a downstream RF carrier using Quadrature Amplitude Modulation (QAM). EdgeQAMs are used for both digital broadcast, and DOCSIS downstream transmission. In a conventional IPTV network system arrangement using M-CMTS architecture, the EdgeQAMs are downstream DOCSIS modulators, and are separated from a core portion of the M-CMTS core. An IPTV server or other suitable IP content provider is coupled to a regional area or backbone network. This backbone network, in turn, is connected to a converged interconnect network (CIN) which also links the M-CMTS core and the EdgeQAMs. The CIN performs as one or more access routers or switches, i.e., devices configured for routing data in an IP network. There is a Layer Two Tunneling Protocol version 3 (L2TPv3) tunnel from the M-CMTS core to the EdgeQAMs, with this tunnel being identified as a Downstream External Physical Interface (DEPI). The IPTV content is carried on the downstream DOCSIS RF carrier from the EdgeQAM to one or more end user network elements, such as a DOCSIS set-top box or an Internet Protocol set-top box (IP-STB). An IP set-top box is a set-top box or other multimedia content processing device that can use a broadband data network to connect to television channels, video streams and other multimedia content. An upstream DOCSIS receiver is coupled to and receives data, such as on-demand commands, from the end user multimedia content processing device. Upstream DOCSIS receivers are combined with or contained within a core portion of the M-CMTS component.
In general, for conventional M-CMTS architecture, all packets traveling upstream or downstream typically travel through the M-CMTS core for appropriate forwarding to the correct network interface or DOCSIS carrier. However, since the downstream DOCSIS modulators (i.e., the EQAMs) are separate from the M-CMTS core, the downstream packets travel from the M-CMTS core, through the CIN, and to the EQAMs on special “tunnel” or “pseudo-wire” connections. These tunnels, which are defined by the Layer Two Tunneling Protocol (L2TP) version 3 (i.e., L2TPv3), are known within the DOCSIS 3.0 standard as Downstream External Physical Interface (DEPI) tunnels, and typically are in the form of gigabit Ethernet fiber links.
One of the features of the DOCSIS 3.0 specification intended to facilitate the use of IPTV content delivery is that the number of downstream EQAMs can be increased independently of the number of upstream DOCSIS data channels. Hence, the downstream DOCSIS capacity can be arbitrarily increased to whatever bandwidth is needed. However, as discussed, downstream IPTV content or data packet flow from the IPTV server to the end user DOCSIS network elements conventionally is required to travel through the CIN to the M-CMTS core, then from the M-CMTS core, on a DEPI tunnel, back through the CIN again, and then on to the EQAM. Such “hairpin” forwarding of downstream data packets back through the CIN requires a disproportionate amount of switching bandwidth and other resources compared to other portions of the system.
Accordingly, there has been a need to provide a bypass architecture that overcomes or avoids the issues involved with data packet flow from the M-CMTS core back through the CIN and then on to the EQAM. Such a bypass architecture might involve or include direct tunneling of video content controlled by and transmitted from a multiple systems operator (MSO) to a downstream modulator, such as a low-cost downstream EQAM, in a manner that bypasses the CMTS, including the M-CMTS core. However, within such a bypass system, to achieve proper bypass, the various MSO-controlled IP content sources, including video servers, would be required to have encapsulation information of DOCSIS framing, as well as tunneling information of the EQAM. However, such IP content sources typically do not have such information. Typically, only the CMTS and CMTS peripherals, such as the EQAM Edge Resource Manager (ERM), have such information. Accordingly, there is a need for a control plane for such bypass systems that allows IP content sources, including video servers, to obtain necessary bypass encapsulation information so that bypass content flows can be properly established with appropriate CMTS quality of service (QoS) support.